Bandgap reference voltage circuits are used to provide stable reference voltages over wide variations in operating temperatures. A common bandgap reference voltage circuit 100 is shown in FIG. 1. The bandgap circuit 100 is typically coupled with a start-up circuit 102. Typically, the main purpose of the start-up circuit 102 is to start the bandgap circuit 100. The start-up circuit 102 may ensure that the bandgap circuit 100 operates within a valid operating range, avoiding any undesired stable state. As a source voltage vdd ramps from zero volts to a final value, the bandgap circuit 100 should reach its desired final value as well.
The amplifier 104 driving the voltage vgcore settles when both inputs of the amplifier 104 are at the same voltage. This occurs when the drop across resistor R1 in FIG. 1 is equal to the difference between the lx and kx diode voltages, i.e.:Icore*R1=νt*ln(k)  (1)The voltage vbg has a zero temperature coefficient whenIcore*R2+Vdiodekx≅1.26V  (2)One of the start-up circuit's 102 functions is to ensure that the bandgap circuit 100 does not remain at a zero-current stable state. To avoid a zero-current stable state, the start-up circuit 102 is provided to initialize the loop, then is effectively removed to avoid an offset error after the bandgap circuit 100 has stabilized.
Embodiments of the invention address these and other limitations in the prior art.